In a previous chapter (see p. 238) it has been stated that when Rubner gave cane-sugar to a dog and measured the metabolism during a period of twenty-four hours the heat production was raised by an increment amounting to about 5 per cent, of the calories ingested. This fact, which has been repeatedly confirmed, does not tell the whole story, because the absorption of the very soluble sugar takes place in the first few hours. Thus Magnus-Levy1 noticed that after giving 155 grams of cane-sugar to a man there was a maximal increase in metabolism of 12 per cent., with a return to the basal level during the fifth hour after taking the food-stuff.

Johansson, Billstrom, and Heijl2 have shown that if 50 to 200 grams of cane-sugar be given a fasting man, the carbon dioxid output increases from 22.6 grams per hour to about 30 grams per hour. The larger ingestion did not produce a higher elimination of carbon dioxid than does the smaller amount. This indicates the evenness with which sugar entering the blood-stream is utilized by the organism. If sugar be present in excess it may be stored as glycogen until it is needed by the cells. The rise in the carbon dioxid output was greater after fructose is ingested than after glucose is given. This was explained as due to the fact that fructose is less readily retained in the liver as glycogen, and therefore reaches the tissues in a larger stream than does glucose under similar circumstances, and hence more completely replaces fat as the source of energy. In a later paper Johansson1 explains that after ingesting 200 grams of glucose containing 740 calories, or one-quarter the man's energy requirement for a day, the rise in carbon dioxid output lasts for six hours and then falls to the fasting basis. This is an indication of the ready absorption and combustion of ingested glucose. If there has been prolonged fasting, ingested glucose may cause no rise in the carbon dioxid output in man on account of its conversion into glycogen. (See p. 273).

1 Magnus-Levy: "Pfluger's Archiv," 1894, lv, 1.

2 Johansson, Billstrom, and Heijl: "Skan. Archiv fur Physiologie," 1904, xvi, 263.

Durig2 gave 100 grams of glucose to a man and compared the metabolism with that obtained after giving 100 grams of fructose. In the latter case the heat production as measured by indirect calorimetry was 10 per cent, greater than in the former; the respiratory quotients were usually higher, being more frequently over unity, and therefore indicating a readier conversion of fructose into fat than was the case with glucose.

Du Bois3 made calorimetric observations on men after giving 100 and 200 grams of glucose and noted the following increases above the basal metabolism:

Percentage Increase In Heat Production After Giving Glucose To Man

1 Johansson: "Skan. Archiv fur Physiologie," 1908, xxi, 30.

2 Togel, Brezina, and Durig: "Biochemische Zeitschrift," 1913,1, 298.

3 Gephart and Du Bois: "Archives of Internal Medicine 1915, xv, 835.

One hundred grams of glucose caused an average increase of 9 per cent, in the heat production and 200 grams one of 12.5 per cent, during three to six hours after their ingestion by a man of 75 kilograms in weight. Ingestion of 200 grams of glucose by a man of 60 kilograms weight caused an increase of 16 per cent, in the heat production. When the larger quantity was administered, the respiratory quotients indicated that the heat production was entirely at the expense of carbohydrate and protein.

The behavior of carbohydrate in many of its details may be best observed in experiments on animals.

Extensive calorimetric observations upon dogs have been carried out in the author's laboratory, and the following principles are believed to have been established:

After giving 50 grams of glucose to a dog Fisher and Wishart1 found an increase in the percentage quantity of blood-sugar at the end of the first hour, and this was followed by a fall to the normal level. A similar phenomenon had been observed in man2 after giving 150 grams of glucose; but in the dog it was further observed that when the sugar solution was given there was at first a considerable reduction in the quantity of urine eliminated. This appears from the following analysis:

Quantity Of Urine As Influenced By Fasting And By Water And Glucose Ingestion

1 Fisher, G., and Wishart: "Journal of Biological Chemistry," 1912, xiii, 49.

2 Gilbert and Baudouin: "Compt. rend. soc. biol.," 1908, lxv, 710.

These authors also found that the hour of the sudden increase in the quantity of urine eliminated coincided with the completion of the absorption of glucose from the gut, and with the last hour of increased metabolism as determined in Lusk's calorimeter experiments. These circumstances led them to investigate the hemoglobin content of the dog's blood. They discovered that although at the end of the first hour there was no alteration in this regard, yet at the end of the second hour, when between two-thirds and three-quarters of the ingested sugar had been absorbed from the intestine, the blood usually became more dilute, as shown by a fall in the percentage amount of hemoglobin. This indicates the continuance of a generous distribution of glucose molecules to the tissues by means of an increase in the volume of the nourishing fluid.

With the cessation of absorption and the return of the blood to its normal volume the metabolism falls to its basal level, the respiratory quotient frequently falls, and there is every indication of a regulation of the carbohydrate supply to the tissues by the liver so that fat and carbohydrate are oxidized together. Only when this food supply is supplemented by carbohydrate from the gut does the metabolism rise. Such an increase may, therefore, be properly termed the "metabolism of plethora." It was furthermore shown that during the period of absorption there was little retention of glycogen by the liver - the absorbed glucose apparently passed freely into the tissues. The largest glycogen content of the liver was found during the last hour of absorption, the last of high metabolism, and the hour characterized by passage of a large volume of urinary water. This was the hour when the liver assumed the duty of arbiter over the carbohydrate supply to the cells.